Some Laws of Mourning for a Grandfather When the Father Does Not Sit Shiva

A person whose grandfather passed away, and the father is in poor health, so the family decided not to inform him of his father's death. Should the grandchildren of the deceased observe some mourning laws as those who mourn with him?

According to the current custom, mourning is observed only for one's father, mother, father-in-law, and mother-in-law, and therefore, it is certainly out of respect for the living father and mother. When the father himself does not mourn, then certainly his children are not required to mourn with him.

Written in Pitchei Teshuva, Yoreh De'ah, Siman 374, s"k 4: "See in Shut Adnei Paz, Siman 11, where it is written about someone whose relative, disqualified from testimony, died elsewhere, and he has mourners here who do not yet know about it, that there is no need to change clothes according to the custom on the first Shabbat. Since the main custom is out of respect for the mourners. And so it implies in the RMA, where it is written out of respect for the mourners with him, therefore here, where they are not mourning, it is obvious that he is exempt, and there is even a prohibition due to disrespect for the honor of Shabbat. And it seems to me that what the RMA wrote, and yet it is customary, refers even to when there are no mourning relatives here, and so it is explained in the DMA, therefore, clothes need to be changed. And as explained, the source of the custom is that today it is customary to mourn only together with one's father and mother, and specifically when mourning for their father and mother, therefore, it is certainly out of respect for one's father and mother, and not out of respect for the deceased, and therefore when they are not alive, even partial mourning is not observed."